[Qgis-user] How to create 3d terrain from DEM?

[Richard McDonnell]

Hi,
Quick glance at your DEM and it looks wrong, you can see the points, which to me suggests there's an issue.

As I don't 100% know the resolution of the original data you are sampling, my advice is limited to a best guess. From what I can see, online, Google elevations are based on Satellite Radar Topographic Mapping (SRTM) and has a resolution of 30m.

You might be better trying to get the original SRTM data from HERE<https://earthexplorer.usgs.gov/>

Alternatively, try using Pixel size values in the IDW Interpolation, setting it to 30 x and 30 y and see what you get.
Kind Regards,

Richard.





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From: QGIS-User <qgis-user-bounces at lists.osgeo.org> On Behalf Of Greg via QGIS-User
Sent: 23 February 2024 04:13
To: qgis-user at lists.osgeo.org
Subject: [Qgis-user] How to create 3d terrain from DEM?

Hello QGIS users,

We have a piece of land in Grand Lake, CO.  We want to build a house on it but the land is on a slope so we need to have a 3D terrain map to locate the house at the optimal location.  I'm mainly going off this video https://www.youtube.com/watch?v=eZZ2MVLZN4o but it doesn't work for me.

I start by making a line string in Google Earth, like this:
[cid:image006.jpg at 01DA663B.609D8310]

Then I save it as .kml file and import that file into GPS Visualizer.  That gets all the elevations along the line.  Then I Convert & add elevation as a plain text file and save the file.

Then in QGIS version 3.28.14-Firenze, I select Layer > Add Layer > Add Delimited Text Layer.  In the popup window, I open the text file and the data gets imported.  The Sample Data looks good.  I select X field as LONG, Y field as LAT, and Z field as ALT.  I leave all the other fields at their defaults and click the Add button.  All the points come in as shown:
[cid:image008.jpg at 01DA663B.609D8310]

Next, I create the DEM by double-clicking the Interpolation > IDW interpolation in the Processing Toolbox.  In the popup dialog, I click the plus button to add a layer and set its Type to Structure lines.  I set the Extent to Calculate from Layer > [name of elevation points].  I set the Rows to 100, leave the rest at their defaults, and click the Run button.  After about 5 seconds it creates a DEM as shown:
[cid:image010.jpg at 01DA663B.609D8310]


Next, I select Basemaps > Google Satellite from the HCMGIS plugin, It loads the image, overlayed on the DEM correctly:
[cid:image012.jpg at 01DA663B.609D8310]
Finally, I click the green tent icon in the in the Qgis2threejs Exporter plugin.

Instead of a nice 3D terrain as shown in the video, I get a wonky image like this:
[cid:image014.jpg at 01DA663B.609D8310]

I've spent a month trying to create a 3D terrain model, without success.  Can anybody tell me what I'm doing wrong, or recommend a workflow that actually works?  Please, no methods that require commercial software such as ArcMap, Rhino, Civil 3D, Autocad, etc.

Thank you!








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